The goal of this research is to provide American industry with the scientific foundation needed to maximize vehicle and fuel performance and efficiency, thereby enabling increased fuel economy and more affordable transportation. For a typical American household, transportation costs are second only to housing expenses.

Increasing the efficiency of internal combustion engines is one of the most cost-effective approaches to improving the energy efficiency of new vehicles in the near- to mid-term in conventional, hybrid, and plug-in hybrid electric vehicles. Researching engines and fuels as a system offers the opportunity to improve the affordability and efficiency of future gasoline engines for American families and businesses.

—Principal Deputy Assistant Secretary for the Office of Energy Efficiency and Renewable Energy Daniel Simmons

The Co-Optima initiative aims to co-develop advanced engine technologies and fuel components with the goal of reducing petroleum consumption by 30% by 2030 beyond what is already targeted. While advanced engine designs are being introduced commercially, they are limited by current fuels. Co-Optima, which launched in October 2015, explores fuel and engine innovations that work together to maximize vehicle performance and fuel economy. The advanced fuel components can be derived from domestic biomass resources.

Blendstocks.The Co-Optima researchers began with a systematic study of more than 400 potential blendstocks from 14 chemical families, providing new insights into the relationship between fuel properties and chemical families. The new report describes the process and interim results of this study.

Based on the interim results, eight representative blendstocks from five chemical families are currently undergoing detailed investigation: alcohols (ethanol, iso-propanol, n-propanol, and iso-butanol); ketones (cyclopentanone); furans (a 40:60 mixture by weight of methylfuran:2,4- dimethylfuran); alkenes (di-isobutylene); and high-aromatics mixtures.

These blendstocks encompass a broad range of structures and properties. The list is no final or limiting. Blendstocks within these five chemical families could be added or removed as more data and information become available.

The representative blendstocks identified in Fuel Blendstocks with the Potential to Optimize Future Gasoline Engine Performance can be blended into gasoline and used in smaller but more powerful and efficient spark-ignition engines, with the potential to be introduced commercially in the 2025–2030 time frame.

Efficiency Merit Function. The research into fuel property impacts on engine efficiency and performance detailed in the first study was guided and informed by a new engine efficiency merit function, or mathematical equation.

The report documents the development of this merit function and how it can be used to improve the scientific understanding of the dynamic relationship between fuel properties, including octane, and engine efficiency.

The benchmark fuel used remains unchanged: an anti-knock index of 87 E10 gasoline with a research octane number (RON) of 91 and a motor octane number (MON) of 83, giving a sensitivity (S = RON - MON) of 8. Assuming that an ethanol mole fraction of 0.21 yields a heat of vaporization (HoV) of 415 kJ/kg, a flame speed (SL) of 46 centimeters per second (cm/s), a lower heating value (LHV) of 42 MJ/kg, a particulate matter index (PMI) of 1.4, and a stoichiometric air-fuel ratio (AFR) of 14.0.

The merit function is intended to be evaluated using the properties of the final, blended fuel, as indicated by the subscript mix. The revised merit function described in the report is:

Under Co-Optima, DOE’s Office of Energy Efficiency & Renewable Energy brings together nine national laboratories, 13 universities, and numerous industry and government stakeholders. Working together, these partners explore technologies with the potential to achieve near-term enhancements to the types of fuels and engines found in most vehicles currently on the road as well as revolutionary engine/fuel technologies that may enable longer-term, higher-impact future solutions. The next phases of Co-Optima will validate these potential fuel efficiency improvements through engine testing and also begin examining fuel efficiency gains in heavy-duty diesel engines.

Resources

• Farrell, John, John Holladay, and Robert Wagner. “Fuel Blendstocks with the Potential to Optimize Future Gasoline Engine Performance: Identification of Five Chemical Families for Detailed Evaluation.” Technical Report. U.S. Department of Energy, Washington, DC. 2018. DOE/GO-102018-4970.

• Miles, Paul. “Efficiency Merit Function for Spark Ignition Engines: Revisions and Improvements Based on FY16–17 Research.” Technical Report. U.S. Department of Energy, Washington, DC. 2018. DOE/GO-102018-5041